1. Field of the Invention
This invention relates to passive barrier elements located on the ground to establish a longitudinal wall that can provide security from terrorist threats by at least slowing, and preferably stopping in a short distance, a vehicle that collides with it, and by providing at least partial protection against blast wave forces, thermal energy, and flying debris from a nearby explosion event.
2. Description of the Related Art
Security zones for protecting sensitive groups of people and facilities, be they private, public, diplomatic, military, or other, can be dangerous environments for people and property if threatened by acts of terrorism. Ground anchored active anti-ram vehicle barriers, bollards, and steel gates may stop a vehicle but do little against a blast wave or blast debris. Earthen berms, sand-filled steel walls, massive concrete or plate steel walls anchored into the ground, or concrete panels laminated with steel sheeting and anchored into the ground have been used to shield against both terrorist vehicles and bombs. But none of these ground-anchored barriers are portable for ease of relocation. Massive barriers of concrete made in segments have traditionally not been strongly coupled together and therefore cannot support high enough tensile forces required to keep a wall from opening up under the force of a straight-on vehicle collision.
Historically, the design of longitudinal barrier systems has focused primarily on issues such as vehicle redirection capability alongside and in divider sections of highways, minimization of vehicle intrusion into a work zone where the vehicle strikes the barrier at a grazing angle, and portability. Many of these barrier systems must be capable of redirecting a variety of different types of vehicles in a smooth and stable manner without causing vehicle rollover; some of these barriers have achieved their design criteria by having high profiles with substantial mass. But the temporary nature of most work zones requires that a barrier system be lightweight and portable so that the barriers can be installed, repositioned, and removed with minimal effort.
Although not relevant to blast protection or stopping straight-on vehicle collisions, some examples of highway barrier wall elements are to be found in the following US patents. U.S. Pat. No. 4,661,010 discloses a roadway defining concrete block held to other blocks a) near their upper portions by U-shaped reinforcement irons cast into the ends of the blocks and linked between blocks using respective threaded vertical pins with nuts to tie to one another by way of a coupling retainer plate and b) near their lower portions by vertically extending pins that link into the bottom end of a vertical tube held in place by the retainer plate. U.S. Pat. No. 4,075,473 discloses a cable-reinforced safety barrier that extends cables through rails and terminates the cables in anchoring means secured to the ground (supporting curb) using bolted fasteners. U.S. Pat. No. 2,907,552 and U.S. Pat. No. 3,210,051 both disclose cabled guardrails wherein the cables used are anchored to the ground at their terminating ends. U.S. Pat. No. 6,767,158 to a “Portable Roadway Barrier” discloses a low-profile barrier formed from an elongated body having an impact surface, a first structure with a key and keyway for fitting adjacent barriers end-to-end to withstand orthogonal and compression forces, and a second structure having support brackets for transferring tensile forces to adjacent barriers, wherein the brackets on adjacent barriers are interconnected with a longitudinally oriented threaded pin. This U.S. Pat. No. 6,767,158 requires the first structure to lie between the second structure and the impact surface. U.S. Pat. No. 5,292,467 to a “Highway Barrier Method” discloses an energy absorbing roadway barrier for dissipating kinetic energy upon impact by a moving vehicle. That barrier has an elongated core of high-density concrete that is anchored to the ground. It has a core that includes prestressed steel rebar members as well as a possibly unstressed central rebar that protrudes from the ends where it can be clamped to those of longitudinally adjacent barriers using a pair of clamping members clamped only to the outside of the rebar. The core is surrounded by a light-weight mixture of cement and sand mixed with such things as polymers and fiberglass. US Patent Application Publication No. 2004/0146347 and U.S. Pat. Nos. 6,413,009; 6,164,865; 5,464,306; 5,443,324; 5,156,485; 5,149,224; 5,134,817; 5,123,773; 5,074,704; 5,011,325; 4,986,042; 4,844,652; and 4,113,400 all disclose various means of keying and/or linking barrier or curbing modules together. US Patent Application Publication No. 2004/0146347 also discloses a plurality of external and continuous cables running the length of the barrier system with which to accommodate longitudinal tension along the entire barrier system. But none of these references include or suggest using a longitudinal cable system running through tunnels within barrier masses aligned longitudinally. None include or suggest using cable systems in a manner that limits accumulation of cable strain from one length-segment of the cable system to another. None include or suggest a way to absorb energy through tensile strain of cables located within barrier masses not anchored to any ground support. And none include or suggest a way to absorb energy through tensile strain of cables but not also absorbing significant energy through bending or shearing of cables. US Patent Publication No. 2004/0146347, in particular, neither discloses nor suggests a motivation or means to enable one barrier element to transfer roll-producing torque about its longitudinal axis to an adjacent barrier element.
None of these barrier systems have focused on protection of a safe side of a barrier wall from encroachment by a high-speed vehicle striking the opposite side of the wall head-on or otherwise at angles that are nearly perpendicular to the wall, and particularly not with portable barrier elements not anchored into the ground. And none of these barrier systems have also focused on the issues of simultaneous protection from both vehicles and explosive blasts.
Forces directed perpendicularly to the longitudinal direction of a continuous wall not firmly tied into the ground, or forces directed at other large angles to the longitudinal direction, must be counteracted both with resisting inertial forces and with longitudinal reaction forces that can be many times higher than the applied forces. In order to resist being displaced too far sideways, even a massive wall must absorb energy by converting kinetic energy (mechanical or aerodynamic), directed perpendicularly or otherwise obliquely to the wall, into other forms of energy, without suffering too much longitudinal strain or lateral shear. Some of the kinetic energy directed against one part of a wall can be transformed to less threatening kinetic energies directed in other directions and at other parts of the wall. Some of the energy can be absorbed as work done to break apart the materials of the wall, preferably without opening up a break in the wall itself, to permanently stretch and distort the wall, and to crush parts of the colliding vehicle. And some of the kinetic energy can be converted to heat created by friction between the parts of the wall, or through pushing, pulling, and dragging of the wall along the ground. Other forms of energy absorption are potential energies of elastic shearing and bending within the wall elements and within the wall system. Another is the conversion of translational kinetic energy into rotational kinetic energy of barrier elements (about vertical and horizontal axes). What is needed is a barrier wall system that exploits all of these energy absorption mechanisms to the best advantage, and in a manner that won't itself endanger life and property.
The kinetic energy involved in a 9,000 kilogram (19,845 lbm) truck traveling at 80 kilometers/hour (49.71 ml/hr) is approximately 2,266,000 joules of energy (approximately 1,671,000 ft-lbf), which is approximately the work performed by one horse in 0.8442 of an hour (50 minutes and 39 seconds), or approximately 0.6296 of a kilowatt-hour. The energies from a nearby explosion can be even more significant and require a strong and robust wall to withstand being moved significantly or otherwise being blown apart. A thousand kilograms of TNT explosive (0.9842 of a ton of TNT) produces approximately 1,845 times the energy of the aforementioned truck. But the energy of exploding that much explosive material may not be as directed as that of a truck, if not ignited too closely to the wall. The shock wave and ensuing high pressures and temperatures, and the high-velocity rush of gas and blast debris, are diminished at any one location away from the blast by virtue of their being spread out over a greater volume of space. For example, if the above explosive were discharged 5 meters from a barrier wall, it could produce an energy, at an area of wall equivalent to that of the frontal area of a truck (approximately 2 meter by 1 meter), of more than 26.6 Megajoules (11.7 times as much as the truck) although with far less inertial mass.
Thus, a need exists for a better barrier wall design than that which uses conventional low or high profile barriers. A need exists for barrier walls that can withstand both head-on collision forces of speeding terrorist vehicles and explosive blasts, and at the same time be rapidly and cleanly deployable and removable. In addition, these walls need to be low cost to manufacture, ship, install, and remove. And they must not endanger underground utilities when being deployed or removed.